Release Notes for MongoDB 2.2


MongoDB 2.2 is a production release series and succeeds the 2.0 production release series.

MongoDB 2.0 data files are compatible with 2.2-series binaries without any special migration process. However, always perform the upgrade process for replica sets and sharded clusters using the procedures that follow.


  • mongod, 2.2 is a drop-in replacement for 2.0 and 1.8.

  • Check your driver documentation for information regarding required compatibility upgrades, and always run the recent release of your driver.

    Typically, only users running with authentication, will need to upgrade drivers before continuing with the upgrade to 2.2.

  • For all deployments using authentication, upgrade the drivers (i.e. client libraries), before upgrading the mongod instance or instances.

  • For all upgrades of sharded clusters:

    • turn off the balancer during the upgrade process. See the Disable the Balancer section for more information.
    • upgrade all mongos instances before upgrading any mongod instances.

Other than the above restrictions, 2.2 processes can interoperate with 2.0 and 1.8 tools and processes. You can safely upgrade the mongod and mongos components of a deployment one by one while the deployment is otherwise operational. Be sure to read the detailed upgrade procedures below before upgrading production systems. [1]

[1] To minimize the interruption caused by election process, always upgrade the secondaries of the set first, then step down the primary, and then upgrade the primary.

Upgrading a Standalone mongod

  1. Download binaries of the latest release in the 2.2 series from the MongoDB Download Page .
  2. Shutdown your mongod instance. Replace the existing binary with the 2.2 mongod binary and restart MongoDB.

Upgrading a Replica Set

You can upgrade to 2.2 by performing a “rolling” upgrade of the set by upgrading the members individually while the other members are available to minimize downtime. Use the following procedure:

  1. Upgrade the secondary members of the set one at a time by shutting down the mongod and replacing the 2.0 binary with the 2.2 binary. After upgrading a mongod instance, wait for the member to recover to SECONDARY state before upgrading the next instance. To check the member’s state, issue rs.status() in the mongo shell.

  2. Use the mongo shell method rs.stepDown() to step down the primary to allow the normal failover procedure. rs.stepDown() expedites the failover procedure and is preferable to shutting down the primary directly.

    Once the primary has stepped down and another member has assumed PRIMARY state, as observed in the output of rs.status(), shut down the previous primary and replace mongod binary with the 2.2 binary and start the new process.


    Replica set failover is not instant but will render the set unavailable to read or accept writes until the failover process completes. Typically this takes 10 seconds or more. You may wish to plan the upgrade during a predefined maintenance window.

Upgrading a Sharded Cluster

Use the following procedure to upgrade a sharded cluster:


Balancing is not currently supported in mixed 2.0.x and 2.2.0 deployments. Thus you will want to reach a consistent version for all shards within a reasonable period of time, e.g. same-day. See SERVER-6902 for more information.


Major Features

Aggregation Framework

The aggregation framework makes it possible to do aggregation operations without needing to use map-reduce. The aggregate command exposes the aggregation framework, and the aggregate() helper in the mongo shell provides an interface to these operations. Consider the following resources for background on the aggregation framework and its use:

TTL Collections

TTL collections remove expired data from a collection, using a special index and a background thread that deletes expired documents every minute. These collections are useful as an alternative to capped collections in some cases, such as for data warehousing and caching cases, including: machine generated event data, logs, and session information that needs to persist in a database for only a limited period of time.

For more information, see the Expire Data from Collections by Setting TTL tutorial.

Concurrency Improvements

MongoDB 2.2 increases the server’s capacity for concurrent operations with the following improvements:

  1. DB Level Locking
  2. Improved Yielding on Page Faults
  3. Improved Page Fault Detection on Windows

To reflect these changes, MongoDB now provides changed and improved reporting for concurrency and use. See locks, recordStats , db.currentOp(), mongotop, and mongostat.

Improved Data Center Awareness with Tag Aware Sharding

MongoDB 2.2 adds additional support for geographic distribution or other custom partitioning for sharded collections in clusters. By using this “tag aware” sharding, you can automatically ensure that data in a sharded database system is always on specific shards. For example, with tag aware sharding, you can ensure that data is closest to the application servers that use that data most frequently.

Shard tagging controls data location, and is complementary but separate from replica set tagging, which controls read preference and write concern. For example, shard tagging can pin all “USA” data to one or more logical shards, while replica set tagging can control which mongod instances (e.g. “production” or “reporting”) the application uses to service requests.

See the documentation for the following helpers in the mongo shell that support tagged sharding configuration:

Fully Supported Read Preference Semantics

All MongoDB clients and drivers now support full read preferences, including consistent support for a full range of read preference modes and tag sets. This support extends to the mongos and applies identically to single replica sets and to the replica sets for each shard in a sharded cluster.

Additional read preference support now exists in the mongo shell using the readPref() cursor method.

Compatibility Changes

Authentication Changes

MongoDB 2.2 provides more reliable and robust support for authentication clients, including drivers and mongos instances.

If your cluster runs with authentication:

  • For all drivers, use the latest release of your driver and check its release notes.
  • In sharded environments, to ensure that your cluster remains available during the upgrade process you must use the upgrade procedure for sharded clusters.

findAndModify Returns Null Value for Upserts that Perform Inserts

In version 2.2, for upsert that perform inserts with the new option set to false, findAndModify commands will now return the following output:

{ 'ok': 1.0, 'value': null }

In the mongo shell, upsert findAndModify operations that perform inserts (with new set to false.)only output a null value.

In version 2.0 these operations would return an empty document, e.g. { }.

See: SERVER-6226 for more information.

mongodump 2.2 Output Incompatible with Pre-2.2 mongorestore